Facing urgent environmental pressure and shortage of energy resources, lots of efforts have been put to shift people life behavior to more environment-friendly and less resources-dependent. Under such situation, electric vehicle (EV) is regarded as an emerging strategic industry in many countries nowadays. Foreseen large amount of EV deployment, there will be great demand for EVCS installation.
It is known that EV charging will dramatically influence a power grid performance without proper control. The electric vehicle ancillary service (AS) supports the transmission of electric power from the electric vehicle to the power grid given obligations of control areas and transmitting utilities within those control areas to maintain reliable operations of the interconnected transmission system. However, if the EVCS can provide certain types of ancillary services to power grid besides just absorbing power to charge an EV, it can not only mitigate a negative impact on grid, but also can enhance the power grid operation stability, and reduce the pressure on grid capacity expansion. The power provided by the electric vehicle ancillary service could be bidirectional, in other words, the power can flow from the electric vehicle to the power grid, and sometimes the power can also flow from the power grid to the electric vehicle. When the EVCS does not provide ancillary service, the power absorbed by the EVCS is determined by the requirement of the electric vehicle demand, and this process belongs to passive response and there is no active regulation in the EVCS. Moreover, when the EVCS provides ancillary service, the power absorbed by the EVCS should consider both the requirement of the electric vehicle and a scheduling requirement of the power grid, in this case, the EVCS has active regulation function in order to improve stability of the power system. In another word, when the EVCS absorbs power from the power grid, it can absorb more power or less power than the EV's requirement in view of the power grid demand; and when the EVCS feeds power to the power grid, it also can regulate the power according to the power grid demand. Through properly designing the control algorithm and implementing in hardware, the ancillary service provision is technically feasible.